During the use of the above mentioned type of firearms, which are meant for rapid and sustained fire, the barrel is subjected to intense heating so that it becomes necessary to disassemble it frequently in order to substitute a new and cold barrel therefor. Such an operation must nevertheless be executed with a maximum simplicity and rapidity so as not to reduce the effective capacity of the weapon.
Already known, for example from U.S. Pat. No. 1,363,262, is a system for removably attaching the barrel to the same automatic portable firearm, which system however does not permit the substitution of an overheated barrel in a manner which is rapid and simple.
In this prior art construction, the assembling and disassembling of the barrel must be effected with a movement which is a combination of a rotational and translational movement of the barrel, so as to detach an arresting tooth which is provided in the rear portion of the barrel, which removal must occur from a recess provided on the frame of the weapon itself. Such a movement of the barrel is always difficult to be carried out, both because of the difficulty of maneuvering and handling the barrel itself when it is overheated and also because of the difficulty of centering the barrel during the assembling thereof due to the fact that the weapon must be held in a firm and steady position. On the other hand the user is forced to modify the normal and conventional position of firing in order to execute this complicated movement of the barrel during the assembling and disassembling operation.
Furthermore, in the arrangements heretofore utilized and known, there is not provided any member or device which might be capable of controlling the position of the carriage and of the firing pin of the weapon during the phase of assembling and disassembling of the barrel and which might be capable of preventing the utilization of the weapon when the barrel is not correctly blocked in place.